Toxic inorganic/organic substances in various water sources have to be reduced below regulated levels before the water goes into drinking water systems or is released into recipients.
Nitrate (NO3−) is a common inorganic contaminant found in groundwater in the areas where agriculture activities occur heavily. Nitrates usually come from fertilizers, used in farming and gardening in order to provide the plants and shrubs with nutrients.
Other contaminants which may be generated from such activities are phosphates (PO43−) and traces of pesticides such as atrazine. Accumulation of fertilizers is a problem as they can go through the soil and contaminate ground water systems. Both shallow water wells and deep water wells can be affected.
Toxic metals such as arsenic (As), chromium (Cr), whereof its oxidation state +6 (CrVI) is regarded as most harmful, lead (Pb), mercury (Hg), cadmium (Cd), selenium (Se), etc, other substances as chlorinated hydrocarbons and other organic substances, sometimes measured as Total Organic Carbon (TOC) are generated either from natural origins or from industrial or farming activities.
Other types of contaminants that may be present in the water are microorganisms, such as bacteria.
A conventional method for killing bacteria is the use of the chlorination process where chlorine containing chemical substances is added to the water for disinfection. Chlorine is a highly efficient disinfectant, however one of the drawbacks with this process is the remaining chlorine compounds in the water, such as CIO− ions which can cause health problems.
In order to reach acceptable levels of contaminants in drinking water, several processes are currently used.
Reverse osmosis is based on the process of osmosis. This involves the selective movement of water from one side of a membrane to the other. This technique is also very energy consuming.
The ion exchange process percolates water through bead-like spherical resin materials (ion-exchange resins). Ions in the water are exchanged for other ions fixed to the beads. Microorganisms can attach to the resins, providing a culture medium for rapid bacterial growth and subsequent pyrogen generation. This technique has a low initial capital investment but a high long-term operational cost.
One of the above techniques is usually applied to target one, or in some cases two contaminants present in the water. This means that several techniques often need to be applied following each other, in a chain process. In order to increase the efficiency, reducing costs, it would be desirable to purify the water from several contaminants in one single step. However, today there are few products available in the market capable of effectively purifying water from multiple contaminants simultaneously.
US patent publication no. 2007/0241063A1 describes a process for treating water contaminated with a volatile organic compound with iron powder granules containing iron, carbon and oxygen.
U.S. Pat. No. 5,534,154 describes a procedure for treating contaminated water by passing the water containing contaminant in solution through a permeable body of treatment material comprising particles of an adsorptive material physically mixed with particles of metal. The iron metal particles mentioned in the patent are iron fillings generally in solid granular form. The procedure requires a negative Eh voltage which in turn demands oxygen exclusion.
U.S. Pat. No. 6,827,757 describes a magnetite-iron based composite with very small average particle size of 0.05-10 μm.
EP 1273371A2 describes an iron powder adapted to remediate selected media by dehalogenating halogenated hydrocarbons in the media comprising iron powder particles and inorganic compounds. Said inorganic compounds should have a very low electric resistivity, and are preferably selected from the group consisting of Ca, Ti, V and Cr. Said inorganic compounds should be present on at least a portion of the surface of each particle.
WO 2008/129551 discloses a liquid filter medium comprising carbonaceous material, a water-insoluble metal oxide or hydroxide, and at least one of chitosan and an ion exchanger.
U.S. Pat. No. 4,642,192 discloses a method of reducing the concentration of inorganic chlorine by passing water through a bed of metal particles, brass. This method shows insignificant effect on reduction of nitrate.
U.S. Pat. No. 6,303,039 discloses a formulation comprising at least two biocide metals and at least one chelating agent, wherein said formulation dissolves over a period of months or longer.
WO 03/076341 describes a system for control of bacterial growth in water comprising antimicrobial treatment media within a containment vessel, the treatment media including one or more of transition metals and transition metal oxides.
U.S. Pat. No. 6,261,986 provides a method for producing a pollutant adsorption and degradation article and the article itself. At least one adsorbent is mixed with at least one pollutant transforming agent to form a mixture. This mixture is compacted to form a porous highly permeable article. Zeolites or surface modified zeolites, SMZ, are proposed as adsorbent and iron powder or iron in combination with other metals such as silver are proposed as pollutant transforming agent. Reduction of chromate and perchloroethylene in water was using the article was demonstrated.
U.S. Pat. No. 6,942,807 provides a water filter device and method which removes heavy metals and organic compounds from raw water. The device comprises at least one iron filter connected in series to a sand filter.
In US 2006/0021946 the use of volcanic rock or recycled minerals from anthropogenic brick to remove toxic metals from contaminated aqueous solutions is disclosed. The volcanic rock or recycled minerals from anthropogenic brick may be combined with zero valent iron, oxidized iron derivates and activated carbon.
The published patent application US 2009/0218266 discloses an ion delivery system, IDS, that comprises a source of metal ions with biocidal properties and a matrix that immobilizes the source of ions and provides a sustained release of ions at biocidal concentrations. Such source may be metal salts, metal particles or particulate metallic alloy. Silver combined with various metals are disclosed. The particle size of the metals or alloys being from 5 to 2 000 nm, preferably under 1 000 nm and most preferably between 100-300 nm.
US 2010/0176044 provides a carbonaceous filtering media for treating drinking water. In some embodiments the filtering media contains silver as an antimicrobial component.
The published application WO2010/019934 provides a process for removing virus from drinking water comprising filtering drinking water through a layer of coarse sand and contacting the drinking water with a composite iron matrix. The composite iron matrix comprises components containing iron, manganese, cerium, carbon phosphorous, sulfur, aluminum silicon, chromium, copper and zinc.